Polyterpene resins are used extensively in adhesive formulations to modify the wettability and tack of the adhesives and are produced commercially by a catalyzed polymerization of various terpenoids. Beta-pinene resins have been produced for many years for use in solvent-based adhesives, but have not found wide application in modem adhesive formulations due to their bimodal molecular weight distributions and relatively high molecular weights.
Attempts to improve the compatibility of beta-pinene-based polyterpene resins with commercially available adhesives and hot melts have met with limited success. Adding mineral oils, dimer oils and plasticizers can improve the rheology, but these tend to reduce the tack and create other problems which diminish the effectiveness of the resin. Catalyst modifiers such as ketones have also been attempted but the resulting resins, while exhibiting lowered softening points, have relatively high levels of bound chlorine and exhibit relatively poor thermal stability in many applications.
It is therefore an object of this invention to provide relatively low softening point beta-pinene-based resins having essentially unimodal molecular weight distributions.
Another object of the invention is to provide a method for making beta-pinene based resins having essentially unimodal molecular weight distributions and relatively low softening points.
Still another object of the invention is to provide beta-pinene-based resins which exhibit improved compatibility in a wide range of currently available hot melt and pressure-sensitive adhesives, especially those containing block copolymers.
An additional object of the invention is to provide beta-pinene-based resins which exhibit a low level of bound chlorine.
With regard to the above and other objects, the invention provides a method for making a low softening point beta-pinene-based polyterpene resin which consists essentially of reacting a mixture containing beta-pinene monomer and an olefinic monomer selected from the group consisting of diisobutylene, 2-methyl-2-butene, dipentene, alpha-pinene and p-menthadiene in the presence of an organic solvent, a Lewis acid catalyst and a co-catalyst at a temperature and for a time sufficient to produce a beta-pinene-based copolymer having a softening point in the range of from about 85.degree. to about 125.degree. C. and an essentially unimodal molecular weight distribution.
In another aspect, the invention provides a beta-pinene-based polyterpene resin consisting essentially of from about 60 to about 95 wt. % beta-pinene monomer units and from about 5 to about 40 wt. % olefin monomer units selected from the group consisting of diisobutylene, 2-methyl-2-butene, alpha-pinene, dipentene and p-menthadiene units. The resin has a softening point in the range of from about 85.degree. to about 125.degree. C., an essentially unimodal molecular weight distribution and a bound chlorine level of less than about 400 ppm.
Because of their essentially unimodal molecular weight distributions, beta-pinene-based polyterpene resins according to the invention are expected to exhibit improved compatibility with A-B and A-B-A block copolymers having styrene end-blocks and conjugated diene midblocks as compared with terpenic resins made using prior methods.
The reaction mixture for production ofbeta-pinene-based polyterpene resins according to the invention contains beta-pinene and olefinic monomers in an organic solvent along with a catalyst and co-catalyst. The beta-pinene monomer may be selected from relatively pure beta-pinene or commercially available mixtures of beta-pinene and other terpenes. A particularly preferred source of beta-pinene is monomer grade beta-pinene monomer which typically contains about 80 wt. % beta-pinene and about 14 wt. % alpha-pinene.
The olefinic monomer to be co-polymerized with the beta-pinene monomer may be selected from the group consisting of diisobutylene, 2-methyl-2-butene, dipentene, alpha-pinene and p-menthadiene. As used herein, "p-menthadiene" means commercial mixtures of dipentene and isomers thereof. Mixtures of two or more of the foregoing olefinic monomers may also be used.
The reaction mixture may contain from about 2:98 to about 50:50 mole ratio of olefinic monomer to beta-pinene monomer with a preferred molar ratio ranging from about 5:95 to about 40:60. It is particularly preferred to have at least about 60 mole percent beta-pinene in the reaction mixture so that the resulting polyterpene will contain at least about 50 to about 60% beta-pinene units by weight.
The catalyst may be selected from one or more Lewis acid catalysts. Of these, aluminum chloride and titanium chloride are preferred with aluminum chloride being particularly preferred. The amount of catalyst relative to monomer in the reaction mixture may range from about 0.3 to about 3 wt. % of the total weight of the monomers with from about 1.0 to about 2.0 wt. % catalyst being particularly preferred.
The co-catalyst may be selected from water, alcohol, an ester and an organohalide of the formula ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 are alkyl or aryl groups containing from about 1 to about 10 carbon atoms and X is a halide selected from chlorine, bromine and iodine. Combinations of two or more co-catalysts may also be used. Examples of tertiary organohalides which may be used as the co-catalyst include tert-butyl chloride and 2-phenyl-2-chloropropane.
Alcohols which may be used as the co-catalyst have the formula ROH wherein R is an alkyl or aralkyl group containing from about 1 to about 10 carbon atoms. Examples of alcohols which may be used include, but are not limited to, methanol, ethanol and the C.sub.10 -terpenyl alcohols commonly found in commercially available terpene hydrocarbons.
The amount of co-catalyst in the reaction mixture should be sufficient to produce a beta-pinene-based resin having an essentially unimodal molecular weight distribution. For example, when water is used as a co-catalyst and assuming no significant amount of other protic co-catalysts are present in the reaction mixture, the amount of water used as a co-catalyst is substantially higher than the amount needed to initiate and sustain a terpene polymerization reaction. Accordingly, when using aluminum chloride as the catalyst, the molar ratios of monomer/AlCl.sub.3 /water in the reaction mixture may be about 1.0/3.1.times.10.sup.-3 to 3.0.times.10.sup.-2 /5.times.10.sup.-4 to 3.0.times.10.sup.-2, and are preferably about 1.0/1.0.times.10.sup.-2 to 2.0.times.10.sup.-2 /2.0.times.10.sup.-3 to 4.0.times.10.sup.-3.
The exact amount of water used may be determined experimentally for a given reaction mixture. If too much water is used, highly chlorinated resins or low yields may result. Accordingly, when water is used as the co-catalyst a molar ratio of co-catalyst to catalyst is from about 1:20 to about 1:1, preferably from about 1:10 to about 1:2.5.
The polymerization reaction is conducted in an organic solvent. Particularly preferred solvents are inert, polar solvents which may be aromatic, haloaromatic or haloalkanes. Especially preferred polar solvents are selected from the group consisting of benzene, toluene, xylene, chlorobenzene and methylene chloride.
Non-polar organic solvents, while not preferred, may also be used in conjunction with a polar solvent. The non-polar solvents may be selected from the group consisting of hexane, pentane, cyclohexane, napthas and olefins which are relatively inert under the conditions involved in the reaction, such as cyclopentene.
The total amount of solvent in the reaction mixture may range from about 60 to about 200 parts by weight per 100 parts total monomer in the reaction mixture, and is preferably from about 80 to about 120 parts by weight of the total monomer. When used with the polar solvent the amount of non-polar solvent in the reaction mixture may range from about 1 to about 50% by weight based on the total weight of solvent in the reaction mixture, and preferably ranges from about 1 to about 10% by weight of the solvent.
The monomeric reactants are added to the reaction mixture in a manner sufficient to provide the desired molar ratios of reactants to catalysts. The monomeric reactants may be added individually to the reaction mixture, but are preferably added as a mixture or blend of monomers.
It is preferred to charge the reaction vessel with the solvent and catalysts and then add the monomers to the reaction vessel over time while stirring the reaction mixture. However, the monomers and catalyst may be added to the reaction vessel essentially simultaneously, particularly when conducting a continuous polymerization reaction.
In a batch reaction sequence, the monomers may be added to the reaction mixture over a period of about 4 hours or more depending on the co-catalyst amount, reaction temperature and amount of co-monomer. In a continuous reaction, residence times of from about 3 to about 5 hours are preferred, although shorter or longer times may be used. The reaction time selected for either the batch or continuous reaction should be sufficient to provide beta-pinene resins having essentially unimodal molecular weight distributions.
During the polymerization reaction, the reaction mixture is maintained under a nitrogen atmosphere at a temperature ranging from about 35.degree. to about 90.degree. C., preferably from about 35.degree. to about 60.degree. C.
After the polymerization reaction is substantially complete, the reaction product mixture is quenched with water and heated to a temperature ranging from about 50.degree. to about 90.degree. C. The aqueous phase is separated from the organic phase by well known phase separation techniques such as decantation, centrifugation, extraction, drying and the like. The separated organic phase may then be washed with distilled water at the elevated temperature to remove traces of catalyst and other impurities.
The solvent is separated from the product by distillation, preferably at atmospheric pressure and under an inert gas atmosphere producing a high yield of low softening point beta-pinene resin. Separation of the solvent is typically conducted at a temperature above about 200.degree. C. depending on the particular solvent used.